Influenza A infections have been described to cause secondary hemolytic uremic syndrome and to trigger atypical hemolytic uremic syndrome (aHUS) in individuals with an underlying genetic complement dysregulation. To date, Influenza B has only been reported to trigger aHUS in 2 patients.In 61% ofaHUS cases, mutations are found in H, B and I factors, membrane cofactor protein (MCP), C3 and thrombomodulin. MCP (CD46) mutations account for 10-15% of cases.

aHUS patients should be screened for all known disease-associated genes. Screening should not be stopped after finding a mutation to avoid missing other genetic susceptibility factors influencing disease phenotype, particularly in patients with MCP or CFI mutations, because they have a higher probability of also carrying mutation in another gene than patients with CFH or C3 mutations. Influenza B is a trigger for aHUS and might be underreported as such. Influenza vaccination may protect patients at risk.